Dysfunction of the vascular endothelium contributes to most cardiovascular, circulatory, and blood diseases. This is not surprising, as the endothelium is the central regulator of hemostasis, vascular development, angiogenesis, vasomotor tone, and the response to vascular injury and inflammation. We have used several complementary approaches during the past funding cycle taking advantage of our longstanding interest in endothelial cell differentiation and gene expression programs to fill in the gaps in our understanding of how endothelial cell destiny and phenotypic diversity are determined. Some of our most exciting findings during the previous funding cycle came from the results of using global gene expression analysis of differentiating endothelial cells to identify candidate genes that are responsible for vascular development. Through this approach, we established a comprehensive list of candidate genes associated with the development of the vascular system during embryonic stem cell differentiation in vivo. Many of the genes we identified in this study were predictable: growth factors, cell surface markers, transcription factors and members of several signal transduction pathways already known to be associated with vasculogenesis. However, we also discovered some new players, including members of the bone morphogenetic protein (BMP) and Wnt signaling pathways. In addition, we identified and cloned the novel endothelial cell precursor-derived protein called BMPER, which has become a major focus of the Specific Aims proposed for our next funding cycle. In this funding cycle, we will explore in more detail the molecular roles of these proteins in modulating endothelial cell phenotypes, with a focus on BMP signaling pathways in the vasculature. The aims of the proposal are to (1) understand the diversity of molecular effects of BMPER in endothelial cells;(2) characterize the diversity of cellular effects of BMPER in endothelial cells;and (3) delineate the role of BMPER in regulation of vascular angiogenic signaling events and inflammation. The scope of this proposal is intended to address relevant biological and physiological questions using state of the art molecular biology techniques. Knowledge gained from this proposal should provide crucial information about endothelial cell development from multipotent precursors, blood vessel formation in health and disease, and endothelial cell-type specific gene expression. In addition, mechanisms for targeted gene delivery to endothelial cells and for disruption and angiogenesis in its pathologic forms may be revealed. PUBLIC HEALTH RELEVANCE: The endothelium plays a critical role in vascular development and pattern formation during embryogenesis, and endothelial cells regulate vessel wall homeostasis, tissue response to ischemia, and vascular regeneration through their effects on vasomotor function and inflammation, angiogenesis, and progenitor cell dynamics. Our overall goal is to determine the events that contribute to vascular differentiation and morphogenesis, with the anticipation that these same processes are recapitulated in angiogenesis-dependent events in the adult.